In a vehicle such as a truck with a body and a frame structure, an axle structure of the full-floating driving wheel type has been widely adopted. In recent driving wheel supporting structures, a double row rolling bearing unit structure has been widely adopted. This improves the readiness of assembly and a reduction of weight and size. One example of such a semi-floating type wheel bearing apparatus of the prior art is shown in FIG. 6.
The wheel bearing apparatus is aimed to reduce the weight and size, prevent the penetration of rain water or dust and prevent the leakage of a differential gear oil. Thus, a wheel hub 51 and a double row rolling bearing 52 are configured as a unit and are connected to a drive shaft D/S. The double row rolling bearing 52 includes an inner member 53, an outer member 54 and double row conical rollers 55, 55 to rollably accommodate between both members 53, 54. The wheel hub 51 has an integral wheel mounting flange 56 to attach with a wheel W and a brake rotor B. They attach at one end of the outer circumference to the mounting flange 56. A cylindrical portion 57 extends from the wheel mounting flange 56 in an axial direction to form the wheel hub 51. Further, serrations 58 are formed in the inner circumference of the cylindrical portion 57 to receive the drive shaft D/S for transmitting torque.
Double row rolling bearing 52 has an outer member 54, a pair of inner rings 60, 60 and conical rollers 55, 55. The outer member inner circumference has double row tapered outer raceway surfaces 54a, 54a. The outer member outer circumference has a body mounting flange 54b that is fixed to an axle housing H. The pair of inner rings 60, 60, is inserted in the outer member 54. Each ring 60 has a tapered inner raceway surface 60a that, in its outer circumference, is formed opposite to the double row outer raceway surfaces 54a, 54a. The double row conical rollers 55, 55 are rollably accommodated between both raceway surfaces 54a, 60a. The pair of inner rings 60, 60 are press-fit into the cylindrical portion 57 formed in the outer circumference of the wheel hub 51. A caulked portion 59 prevents removal of the inner rings 60 in the axial direction with respect to the wheel hub 51. The caulked portion 59 is formed by plastic deforming an end portion of the cylindrical portion 57 in the radial direction. Thus, the forward end surface of the pair of inner rings 60, 60 are set in an abutting configuration as a so-called back-abutted type double row conical roller bearing.
A cap 61 is press-fit in an opening of the wheel hub 51. The cap 61 includes a metal core 61a and an elastic member 61b. The metal core is made of a steel plate that is press-formed, into a substantially “C”-shaped cross-section, from an austenitic-stainless steel sheet (JIS SUS 304 etc.) or preserved cold rolled steel sheet (JIS SPCC etc.). The elastic member 61b is rubber and is bonded, via vulcanization, to at least the fitting portion of the metal core 61a. The elastic member 61b is elastically deformed into the fitting surface to fluid-tightly seal the inside. Accordingly, it is possible to completely prevent leakage of the differential gear oil to the outside and the penetration of rain water or dust from the outside into the drive shaft. This prohibits mixing of the water or dust into the differential gear oil. In addition, the cap 61 is almost uninfluenced by the elastic deformation of the wheel hub 51 even though the wheel hub 51 repeatedly receives a moment load and is elastic deformed when driving the vehicle. (See Japanese Laid-open Patent Publication No. 2005-297944.
However, in the wheel bearing apparatus of the prior art, there are concerns that rain water or dust from the outside may penetrate through a gap between the axle housing H and the double row rolling bearing 52. Thus, the differential gear oil may leak outside. In this case, the rain water or dust is mixed with the differential gear oil and the leaked differential gear oil leaks into the surroundings.